clang -O2  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations unistd/getpgid.c -o unistd/getpgid -D_POSIX_C_SOURCE=202405L  -lm  -lintl
unistd/getpgid.c:5:23: error: use of undeclared identifier 'getpgid'
pid_t (*foo)(pid_t) = getpgid;
                      ^
1 error generated.